The present invention relates to electronically controlled throttles for vehicle engines and in particular to a high reliability throttle controller using redundant throttle signals.
A throttle controls the flow of air, or air and fuel, inducted into an internal combustion engine, and thereby controls the power produced by the engine. Engine power defines the speed of the engine or vehicle to which it is attached, under a given load condition, and thus, reliable control of the throttle setting is important.
In prior art mechanical systems, a direct mechanical linkage controlled the throttle, typically in the form of a cable running from the accelerator pedal, operable by the user of the automobile, to the throttle valve. Absent tension on the cable from the pedal, the throttle valve would revert to an idle opening under the influence of a biasing spring. The idle opening provides sufficient inducted air and gas to permit low speed operation of the engine under no- or low-load conditions.
Although mechanical linkages are simple and intuitive, they are not readily adapted to electronic control of an engine such as may be desired in sophisticated emissions reduction systems or for features such as automatic vehicle speed control. For these purposes, the mechanical linkage may be replaced with electrical wiring carrying throttle signals from a position sensor associated with the accelerator pedal to a throttle controller operating a motor actuating the throttle valve. The throttle signal may be monitored for loss or faults to provide greater reliability to the system.
It is desirable that any faults in the throttle signal be minimized to avoid disabling the vehicle unnecessarily. One method of reducing such faults is by using redundant throttle signals conveyed through separate control channels. If one channel fails, the non-faulted channel may be used to provide continued control to the engine. If both channels fail, the throttle is moved to a safe state.
Such systems may nevertheless be subject to conditions, such as intense electromagnetic interference, which can cause faults in both channels disabling them and causing a loss of availability of the throttle control.
The present inventors have recognized that under certain circumstances, a faulted control channel may be rehabilitated once the fault is gone to provide substantially increased availability. Such rehabilitation creates a possibility of a sudden change in throttle plate position if the rehabilitated channel provides a throttle setting different from that currently in effect. This problem is addressed by a procedure which smoothly changes from one throttle setting to another in a xe2x80x9crampingxe2x80x9d when a control channel is rehabilitated, thus preventing abrupt changes in engine power.
Specifically, the present invention provides a throttle control for a vehicle engine where the throttle control has an input for receiving a first and second redundant throttle signal providing throttle settings. A fault detection circuit communicates with the inputs to detect a fault, if any, in at least one of the first and second redundant throttle signals. A throttle signal processor receives information from the fault detector and the inputs and operates to (1) in the absence of a fault in at least one of the first and second throttle signals, to provide a normal throttle setting determined from the throttle settings of at least one of the first and second throttle signals, and (2) upon recovery from the fault of at least one of the first and second throttle signals, to produce a throttle command gradually transitioning between a fault throttle setting used during a fault of at least one of the first and second throttle signals and the normal throttle setting.
Thus it is a first object of the invention to permit the rehabilitation of faulted inputs in the throttle signals without creating an abrupt transition in vehicle power or speed. The gradual transition between the fault throttle setting and the normal throttle setting allows reaction and compensation by the operator of the vehicle.
Upon a fault of the first and second throttle signals, the fault throttle setting may produce an output signal adjusting the throttle to a setting within the idle range of the engine.
Thus it is another object of the invention to provide for operation of the vehicle but at a reduced capacity in the event of a complete failure of the throttle signals.
Alternatively, the fault throttle setting may be determined from a throttle setting of the non-faulted one of the first and second throttle signals when only one of the first and second throttle signals has failed.
Thus it is another object of the invention to provide for continued operation during a failure of one signal yet with the gradual recovery described above when the signal is rehabilitated.
Alternatively or in addition, the fault throttle setting may be used when the first and second throttle signals deviate in value by an amount greater than a predetermined deviation amount and the fault throttle setting may be determined from the first and second throttle signals associated with the lower throttle setting.
Thus it is another object of the invention to detect possible faults indicated by deviation in the values of the throttle signals and to adopt the more conservative throttle signal as the fault throttle setting.
The fault throttle setting may be produced only when the fault condition exceeds a predetermined time.
Thus it is another object of the invention to allow continued throttle operation for extremely short, intermittent fault situations.
The throttle setting when neither the first nor second throttle signal is faulted may be based on a preferred one and only one of the first and second throttle signals.
Thus it is another object of the invention to provide a simple method of converting redundant throttle signals into a single throttle setting.
The throttle signals may be a series of pulses whose widths represent throttle settings. The fault detection circuit may indicate a fault when either the frequency of the pulses or their width exceeds a predefined range.
Thus it is another object of the invention to provide a redundant fault detection system such that provides good assurance that when no fault is detected, that the signal may be rehabilitated for use in controlling the throttle.
The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessary represent the full scope of the invention, however, and reference must be made to the claims herein for interpreting the scope of the invention.